The present invention is directed to an improved solderless metallurgical joint and in particular, to novel methods and apparatus for completing a metallurgical joint between copper and aluminum tubes.
The factors necessary to produce a metallurgical joint or bond between copper and aluminum are well known. For example, it is known in the art that minimal oxides should be present on both of the metals at the area or point where the metals are joined together. It is also known that a mechanical pressure is necessary to provide close proximity at all points where the metals are to be joined. Finally, it is known that heat at the boundary of the copper and aluminum at the proper temperature is necessary to provide a metallurgical bond between the two metals.
At present, there are several methods known for providing a metallurgical bond between copper and aluminum. For example, Japanese Patent 54/133450 discloses the technique of butt welding copper and aluminum tubes or pipes together. This method is based upon the mechanical pressure and frictional heat build up between the tube ends to form a butt weld joint. Additionally, U.S Pat. No. 3,633,266 discloses a process which requires a solder coating on the joint defining surface between the copper and aluminum tubes. The heating and the telescopic pressure movement of the tubes relative to one another breaks up the oxide coating on the solder coating and facilitates a body between the outside and inside surfaces of the copper and aluminum tubes. The resultant joint includes a solid coating of a solder positioned on the joint defining surfaces between the two metals. Also, it has been suggested that copper and aluminum sheets may by rolled and pressed together to produce a bonded sheet material. From this sheet material, copper and aluminum bonded tubes are drawn. This process is an expensive and time consuming operation.
The above described techniques and methods for providing a metallic joint between copper and aluminum tubes have failed to provide uniform and linear metallurgical joints or bonds between the copper and aluminum. For example, in the butt weld process, the thickness of the joint is limited to the width of the wall thickness of copper and aluminum tubes. Accordingly, it is often times necessary that the wall width or thickness be increased by using various swaging techniques to provide sufficient weld area. However, the weld area available when using the butt weld process is generally less than 0.075 inches in width. To produce heavier or thicker tube walls prior to butt welding, additional manufacturing steps are required, which steps require additional apparatus, are time consuming and very expensive.
Additionally, many of the steps necessary for depositing a solder coating between the aluminum and copper tubes, are eliminated, such as the preparation by swaging of the aluminum tube and the sonic timing using zinc or the aluminum and or copper tubes or the copper tube alone are time consuming and expensive operations. The prior art processes for completing the solder coating metallurgical joint requires the joining of copper and aluminum which require dipping of the joint or tube ends vertically into the molten zinc, a process which limits orientation options during manufacturing. Finally, the production of flashing in the tubes from butt welded joints and the use of solder coatings or zinc, in the sonic tinning process, often times leaves debris inside the tubes which cause rapid failure of the compressor during heat exchanger operations.